1. Technical Field
The technical field relates to a method for preparing polyarylene sulfide (PAS) monomer.
2. Description of the Background Art
Polyarylene sulfide (PAS), specifically polyphenylene sulfide (PPS), is a material with good mechanical properties and excellent thermal and chemical resistance compared to metals of the electronic and automobile industry. PAS is also useful in spinning fibers of filters, connectors, coating material, and electronic components. Conventionally, the preparation of PAS was formed by reacting p-dichlorobenzene and sodium sulfide as monomers. A massive byproduct of alkali metal halide resided in the PAS resin, so the PAS resin needed some purification steps. However, the purification by removal of the byproduct increases the production cost, degrades the quality, and decreases the efficiency of the production of PAS resin.
JP 07-304872 A discloses that the monomeric cationic intermediate of polyphenylene sulfide (PPS), including a sulfonium group, was prepared by combining thioanisole and methylphenyl sulfoxide by an electrophilic substitution mechanism in an acidic condition, and this intermediate was demethylated to obtain a neutral dithioether compound as shown by (1) in the reaction scheme below. Subsequently, Br2 and KHCO3 were introduced to oxidate the neutral dithioether compound to obtain a PPS monomer with a sulfoxide group after purification as shown by (1) in the reaction scheme below. Then, the PPS monomer is reacted in an acid to obtain a polysulfonium intermediate, and the polysulfonium intermediate is demethylated to obtain a neutral PAS resin as shown by (2) in the reaction scheme below.

However, the use of a halogen such as Br2 for oxidation is disadvantageous. Specifically, the halogen results in increased cost due to the additional steps needed to purify the PAS resin. In addition, the halogen is not environmentally friendly. Therefore, an industry-wide need exists for a method of preparing a polyarylene sulfide monomer without a halogen.